Fine morphology of four Licmophora (Bacillariophyta, Licmophorales) species from Admiralty Bay and Elephant Island, Antarctic Peninsula
Luciano F. Fernandes1, Mariana Calixto-Feres1, Denise Rivera Tenenbaum2, Leticia K. Procopiak, Danielle Portinho & Friedel Hinz3
1 Universidade Federal do Paraná. Departamento de Botânica, C.P. 19031, CEP 81531-900.
Paraná, Brazil luc.felicio@gmail.com
2 Universidade Federal do Rio de Janeiro, Laboratório de Fitoplâncton Marinho, Avenida Professor Rodolfo P. Rocco, 211, Prédio CCS, Bloco A, Sala A1-61, Ilha do Fundão, CEP: 21949-900, Rio de Janeiro, Brazil.
3Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany Recebido em 06.XIII.2013. Aceito em 20.XI.2014
RESUMO – Morfologia fi na de quatro espécies de Licmophora (Bacillariophyta, Licmophorales) da Baía do Almirantado e Ilha Elefante, Península Antártica. Neste artigo, quatro espécies da diatomácea bentônica da Antártica, L. antarctica M. Peragallo, L.
belgicae M. Peragallo, L. gracilis (Ehrenberg) Grunow e L. luxuriosa Heiden, são descritas em microscopia eletrônica, baseado em duas coleções de amostras obtidas durante diferentes expedições do Programa Antártico Brasileiro (verão de 1994, e 2003 a 2010). Amostragens do plâncton e bentos foram realizadas em diferentes locais da Ilha Rei George e Ilha Elefante, Península Antártica. Três espécies endêmicas, L. antarctica, L. belgicae e L. luxuriosa, são descritas, incluindo informação sobre estruturas como rimopórtula, poróides e multiscissura.
L. gracilis também foi examinada para confi rmar sua identidade. Comparações com espécies próximas também são providenciadas, bem como a distribuição na Península Antártica.
Palavras-chave: diatomáceas bentônicas, taxonomia, ultraestrutura.
ABSTRACT – In this paper, four Antarctic species of the diatom genus Licmophora namely L. antarctica M. Peragallo, L. belgicae M. Peragallo, L. gracilis (Ehrenberg) Grunow and L. luxuriosa Heiden are described using an electron microscope, based on two collections of samples collected during different expeditions under the Brazilian Antarctic program (Summer of 1994, and 2003 to 2010). Plankton and benthic samplings were carried out at different locations in King George and Elephant Islands, Antarctic Peninsula. The fi ne morphologies of three endemic species, L. antarctica, L. belgicae and L. luxuriosa, are described, including information on structures like rimoportula, poroids and multiscissura. L.
gracilis was also examined for confi rmation of its identity. Comparisons with allied species are also provided, as well as their geographic distribution around the Antarctic Peninsula.
Keywords: benthic diatoms, taxonomy, ultrastructure.
INTRODUCTION
Licmophora C. Agardh, 1827 is a benthic diatom genus widespread in coastal marine environments around the world (Honeywill 1998, Witkowski et
al. 2000, Al-Handal & Wulff 2008a, 2008b, Lobban et al. 2011). Its species can thrive in different substrates like sediments, rocks, macroalgae, skin of vertebrates, and ice. The main features of Licmophora are heteropolar cells attached to the substrate by
mucilage tubes, frustules with 2-3 rimoportulae, and clavate or spathulate valves pierced by uniseriate striae, surrounding a narrow sternum. Usually, there are 1 or 2 rimoportulae per valve, having an internal labiate structure and it is externally fl ush, with a round or elongate opening. At the foot pole, a number of elongate slits constitute the multiscissura (sensu Honeywill 1998). Additionally, the valvocopula is septate in most of the species.
According to VanLandingham (1971), about 58 species have been described so far worldwide. After this review, four new species were added: L. pinnulata Ricard (1975), L. unidenticulata Takano (1983), L.
fl ucticulata Lobban et al. (2011) and L. comnavmaria Lobban & Schefter (2013). L. normaniana (Greville) Wahrer was transferred from Campylostylus normanianus to the genus Licmophora (Wahrer et al. 1985). Comparatively, few investigations using electron microscope were developed to study frustule ornamentations in Licmophora (see literature in Gaul et al. 1993, Henderson & Reimer 2003). Modern investigations focused on the ultrastructure of a few species, already elucidating important diagnostic structures in Licmophora. (Montgomery 1978, Takano 1983, Wahrer et al. 1985, Sar & Ferrario 1990, Round et al. 1990, Honeywill 1998, Terasaka et al. 2005, Lobban et al. 2011, Lobban & Schefter 2013, Lobban 2013). Honeywill (1998) offers a comprehensive survey of the genus in Britain, describing 15 species of Licmophora in both scanning and transmission electron microscopes. Moreover, the author identifi ed and illustrated different types of velum covering the areolae, as well as proposed the utilization of multiscissura as a valuable taxonomic character in the genus.
In Antarctica, about 11 valid species were recorded: L. antarctica Carlson, L. belgicae M.
Peragallo, L. charcotii M. Peragallo, L. gigantea Mereschkowsky, L. rouchii M. Peragallo, L. luxuriosa Heiden, L. plana Heiden, L. pseudohyalina Frenguelli
& Orlando, L. gracilis (Ehrenberg) Grunow, L.
abbreviata Agardh, and L. onassis Hustedt (Agardh 1827, Van Heurck 1909, Peragallo 1921, Hustedt 1952, 1958, Frenguelli & Orlando 1958, Simonsen 1992). Simonsen analyzed the types of Heiden in Heiden & Kolbe (1928), giving illustrations of L.
belgicae (as L. decora), L. luxuriosa and L. plana.
All the species were collected from diverse benthic habitats, especially rocks and macroalgae. Recently,
Al-Handal & Wulff (2008a, 2008b) recorded four species in Potter Cove, King George Island, describing their frustules in light microscope. To our knowledge, the only paper using electron microscopy for the description of species in Antarctica is Ahn et al. (1994) for L. belgicae (identifi ed as L. luxuriosa).
In this paper four species of Licmophora found in King George and Elephant Islands, Antarctic Peninsula are described in electron microscopy, L.
antarctica M. Peragallo, L. belgicae, L. gracilis, and L. luxuriosa. This contribution is part of a project investigating the taxonomy of benthic diatoms in Admiralty Bay and nearby, from which other papers were already published (Fernandes & Procopiak 2003, Procopiak & Fernandes 2003, Fernandes et al.
2007, Fernandes & Sar 2009).
MATERIAL AND METHODS
The material examined in this study came from two scientifi c collections, sampled during different periods and in different environments (Tab. 1).
The fi rst sampling was carried out during the XIII Expedition of the Brazilian Antarctic Program (PROANTAR XIII) in November and December of 1994 (Tab. 1), in different locations in Admiralty Bay, King George Island and in Elephant Island.
Both islands are in the South Shetland Islands, Antarctic Peninsula. In Admiralty Bay (62°05’S, 58°35’W) fi ve benthic samples were obtained in the intertidal and infralittoral zones by autonomous diving (SCUBA). The sampling points were located near the Brazilian Antarctic station. Cells were removed from small rocks by scrapping the surface with a fi ne tooth brush. The same methodology was used on Elephant Island (61°00’S, 65°30’W). In this site, sampling was carried out in the intertidal zone only; a total of eleven samples were collected.
The second collection was gathered during the expeditions sponsored by the Brazilian Antarctic Program spanning from 2003 to 2010 in December, February and March. Plankton samples were collected in seven oceanographic stations (Tab.
1) using a plankton net with 20 µm mesh size.
All material was preserved in formalin at the fi nal concentration of 2%. Samples of both collections are deposited in the UPCB Herbarium of the Federal University of Paraná State, Curitiba, Paraná, Brazil.
Table 1. Data of samples collected in different sites and algal communities (epilithon or phytoplankton) in Admiralty Bay (King George Island) and Elephant Island, Antarctic Peninsula. The occurrence of species in the samples is also showed, and indicated as follows: A (Licmophora antarctica M. Peragallo), B (L. belgica), G (L. gracilis) and L (L. luxuriosa).
Table 1. Continuation
Preparation and Observation of Samples
Preparation for analysis in light and electron microscopes followed the technique by Hasle &
Fryxell (1970). Permanent slides were mounted with Naphrax resin (refractive index = 1.74, Northern Biological Supplies). Valves were measured and photographed using an Olympus BX-51 light microscope (LM) equipped with phase contrast.
For scanning electron microscope (SEM), small drops of cleaned samples were placed on aluminum stubs and sputter-coated with gold (Balser DSC300) for observation with a Jeol-JSM 6360LV electron microscope at 15kV acceleration voltage and 8mm
work distance. A few samples were mounted on a 150 mesh grid covered with formvar/carbon (Electron Microscope Supplies, USA) for examination in transmission electron microscopy (TEM) in a Jeol JM1200 EXII at 80 kV acceleration voltage.
Systematic treatment followed Round et al.
(1990). Terminology was based on Ross et al. (1979), Cox & Ross (1980), Barber & Haworth (1981), and Honeywill (1998).
RESULTS
A total of four species of Licmophora were recorded, most occurring in all samples in both
Admiralty Bay and Elephant Island (Tab. 1). The species are described below.
Licmophora antarctica M. Peragallo, Deuxième Expédition Antarctique Française, Botanique, p. 70, pl. 4, fi g. 10, 1921.
(Figs. 1-9)
According to VanLandingham (1971), the name L. antarctica M. Peragallo (1921) is not valid, since there is a different species, L. antarctica Carlson (1913 in Süsswasser-Algen aus der Antarktis, Süd- Georgien und den Falkland Inseln, n.14, p.30, pl.3, fi gs 23, 24), described previously. Thus, this latter
has the priority by the publication date. Taking into account that our material corresponds to the species described in Peragallo (1921). We provisionally use Peragallo’s name until further nomenclatural investigations clarify its identity.
References: Peragallo (1921, p. 70, pl. 4, fi g. 10), Frenguelli & Orlando (1958, p. 111, pl. 5, fi gs.1-2), Peragallo (1921, p. 70, pl. 4, fi g. 10), Al-Handal &
Wulff (2008b, p. 57, fi g. 8, but corresponding to L.
antarctica Peragallo)
LM Description: Valves are heteropolar, spathulate with rounded apices (Fig. 1); 62-160 μm apical axis, 7-9 μm transapical axis. Striae are uniseriate, 6-10 in 10 µm, opposite to slightly alternate. Each stria
Figs. 1-9. Licmophora antarctica. LM and SEM images. 1. valve surface (LM); 2. Frustule in girdle view (LM); 3. External view of whole valve; 4, 5. Internal view of valves; 6. Internal view of head pole with sessile rimoportula located in the intersection of valve surface and mantle; 7. Internal view, detailing the foot pole with large rimoportula on valve surface; 8. External view of foot pole.
Note slit of rimoportula; 9. Internal view of foot pole lacking rimoportula. Multiscissura is visible in the mantle edge. Bars: 1-5 = 10 µm; 7 = 2 µm; 6, 8 = 1 µm; 9 = 5 µm.
has 14-18 rounded areolae in 10 µm. Sternum is very narrow, running the entire valve surface (Fig.
1). Three rimoportulae per frustule are present;
rimoportula of the head pole diffi cult to observe, smaller than the basal one. Cingulum has 2-3 bands per theca (Fig. 2)
SEM Description: The striae are composed of rounded to slightly elliptical areolae (Figs. 3-9).
Internally, the virgae are thicker than vimine (Figs.
6-7). At the foot pole, small pores are located between the striae and the multiscissura (Figs. 7-8). The basal rimoportula, when present, is a large elongated labiate structure, transapically oriented, on the inner side of the valve surface (Figs. 5, 7), opening to the outside through a small slit (Fig. 8). The apical rimoportula opens internally through a very short stalked labiate structure elongated in apical direction, located at the intersection of the valve surface and the mantle (Fig.
6), and is externally slit-like. The multiscissura has 14-16 slits (Figs. 7, 9).
Ecology and distribution: epiphytic, accidental in the plankton; also recorded in bottom sediments (Al-Handal & Wulff 2008a). West of the Antarctic
Peninsula: Margarita Bay, Kappa and Observatory Bay. North of the Antarctic Peninsula: King George Island (Frenguelli & Orlando 1958, Al-Handal &
Wulff 2008b).
Licmophora belgicae M. Peragallo, Deuxième Expédition Antarctique Française, Botanique, p. 70, pl. 4, fi gs. 5-6, 1921.
(Figs. 10-20)
References: Peragallo (1921, p. 70, pl. 4, fi gs. 5-6), Frenguelli & Orlando (1958, p. 112, fi gs. 8-10), Hustedt (1958, p. 138), Simonsen (1992, p. 28, pl.
24, fi gs. 1-5 as L. decora), Cremer et al. (2003, p. 95, fi g. 97, as L. decora).
LM Description: The valves are heteropolar, clavate with rounded apices (Figs. 10, 11) and a slight constriction at the foot pole; 78-131 µm apical axis, 11-18 µm transapical axis. Striae are uniseriate and transverse; 10-12 in 10 µm. Areolae are rounded, 16- 20 in 10 µm. Sternum narrow. Virgae are irregular with different widths (Fig. 11). Three rimoportulae per frustule are present. The apical rimoportula is placed between the mantle and valvar surface. The rimoportula at the foot pole is larger than the one at
Figs. 10-20. Licmophora belgicae. LM and SEM images. 10, 11. valves (LM);
11. Note rimoportula in each pole of valve; 12. External view of head pole showing slit of rimoportula; 13, 14.
Labiate structure of head pole rimoportula in internal view; 15, 16. Internal views of foot pole, illustrating the presence (15) and the absence (16) of rimoportula, multiscissura is visible in the mantle; 17. External view of foot pole lacking rimoportula, note bands of cingulum; 18-20. Cingular bands; 18. Valvocopula with shallow septum (arrow);
19, 20. Striated valvocopula (VC) with septum (S) and hyaline strip (arrow), and longitudinally striated 2nd (2B) and 3rd (3B) bands.
Bars: 10, 11 = 10 µm; 12-14, 16-20 = 5 µm; 15 = 1 µm.
the head pole, and is located on valve surface (Fig.
10).
SEM Description: Valves have transverse striae composed of rounded to slightly elongate areolae (Figs. 12-17). Virgae are thicker than vimine (Figs. 14, 15). The foot pole has small rounded pores between the larger striae and the multiscissura (Figs. 15, 16).
A group of radiate striae is present at the margin of the head pole (Figs. 12-14). A basal rimoportula, when present, is located at the end of the sternum;
internally, the labiate structure is shortly stalked, transapically oriented, located near the fi rst striae (Fig. 15). The apical rimoportula is located between the mantle and valvar face; it opens externally by a slightly elongated slit (Fig. 12), coarser than the areolae and has an internal labiate structure, sessile and elongate in the apical direction (Fig. 14). The multiscissura has 18-24 slits (Figs. 15-16). The cingular bands are open; areolate (Figs. 17-20). The valvocopula is ligulate and has a rudimentary septum (Figs. 18-19) with 30-34 transverse striae in 10µm
(Fig. 19). The remaining two bands have two rows of poroids running in apical direction (Figs. 19, 20).
Ecology and distribution: epiphytic, accidental in the plankton. Recorded North of the Antarctic Peninsula: King George Island; West of the Antarctic Peninsula: Pettermann Island (Peragallo 1921, Hustedt 1958, Frenguelli & Orlando 1958, Krebs 1983, Ahn et al. 1994 (as L. luxuriosa), Cremer et al. 2003).
Licmophora gracilis (Ehrenberg) Grunow, Botanischer Theil, Algen, p. 34, pl. 17, fi g. 6, 1867.
(Figs. 21-34)
References: Grunow (1867, p. 34, pl. 17, fi g. 6), Frenguelli & Orlando (1958, p. 112, pl. 4, fi gs. 38- 42), Honeywill (1998, p. 239, fi gs 9a-h), Witkowski et al. (2000, p. 65, pl. 18, fi gs. 12-15, pl. 19, fi gs.
7-15), Cremer et al. (2003, p. 95, fi gs. 98-99), Al- Handal & Wulff (2008a, p. 58, fi gs. 29-30).
LM Description: The valves are heteropolar, spathulate (Figs. 21-23), or clavate (Figs. 30, 31) with rounded apices; 21-69 µm apical axis, 5-10 µm
Figs. 21-29. Licmophora gracilis. Spathulate valves in LM and SEM. 21-23. small specimens (LM). Note rimoportula in 21 and 23 (arrows); 24. Whole valve in internal view; 25, 26. Head poles in internal view; rimoportula is short stalked; 27. Head pole in external view with a rimoportula slit; 28. Detail of foot pole in external view showing rimoportula slit and multiscissura; 29. Labiate structure of inclined rimoportula at the foot pole in internal view. Bars: 21-23 = 10 µm; 24 = 5 µm; 25-29 = 2 µm.
transapical axis. The foot pole is somewhat rostrate.
Striae are delicate and uniseriate, 16-26 in 10 µm.
The virgae are arranged irregularly over the valve surface. The sternum is very narrow (Fig. 22). Two rimoportulae per frustule are present; one in the foot pole of one valve and the other in the head pole of the other valve (Figs. 21, 23, 30, arrows).
SEM Description: The valves have transverse striae composed of 16-20 areolae in 10 µm (Figs. 24, 32). Areolae are rounded (Figs. 25, 33) to slightly elongated (Fig. 26) in the transapical direction. The rimoportula of the head pole is labiate and stalked, transapically oriented (Figs. 25-26) in inner view;
opened through an elongated slit on the valvar surface, externally (Fig. 27). At the foot pole, the rimoportula is located on the valve surface, internally it is labiate and short stalked, transapically oriented (Figs. 29, 33, 34), being larger than the one at the head pole. Its external aperture is an elongated slit (Fig. 28). The multiscissura is composed of 7-9 slits (Figs. 28, 29, 34). The valvocopula has a rudimentary septum.
Ecology and distribution: epiphytic and growing on sediments, accidental in the plankton (Al-Handal
& Wulff., 2008a). The species was recorded west of the Antarctic Peninsula: Port Melchior, Kappa and Observatory Bay and north of the Antarctic Peninsula:
King George Island (Frenguelli & Orlando 1958, Al-
Handal & Wulff 2008a). It is a common species in Europe and Arctic coas ts (Witkowski 2000).
Licmophora luxuriosa Heiden in Heiden & Kolbe, Botanik, v. 8, n.5, p. 572; pl. 6, fi gs. 140, 141, 1928.
(Figs. 35-44)
References: Heiden & Kolbe (1928, p. 572, pl. 6, fi gs. 140-141), Hendey (1937, p. 337), Simonsen (1992, p. 28, pl. 25, fi gs. 1-7, pl. 26, fi gs. 1-3), Al- Handal & Wulff (2008b, p. 429, fi gs. 9-15).
LM Description: Valves are heteropolar, clavate with rounded apices (Figs. 35, 36); 41-109 µm apical axis, 11.5-19 µm transapical axis. Transverse striae are uniseriate and robust; 5-7 in 10 µm, composed of delicate areolae. The sternum is straighter and wider (Fig. 35) than other species. Three elongated rimoportulae are present in the frustule. In the case of a valve presenting one rimoportula, this structure occurs in the head pole. In valves having two rimoportulae, the one located in the foot pole is larger than the one at the head pole (Figs. 35, 36, arrows).
SEM and TEM Descriptions: Valves have transver- se striae (Fig. 37) composed of 44-55 areolae in 10 µm. Striae in the head pole become strongly radiate (Figs. 38, 43). Virgae are large, coarsely silicifi ed in- ternally (Figs. 38-40). The areolae are elongated in
Figs 30-34. Licmophora gracilis. 30, 31. (LM) and 32-34 (SEM); 30. Valve in bright fi eld with a large rimoportula at foot pole (arrow);
31. Same valve in face contrast; 32. Whole valve in internal view; 33, 34. Internal views of foot pole detailing slightly different rimoportulae, and multiscissura. Bars: 30-32 = 10 µm; 33-34 = 2µm.
the apical direction, juxtaposed (Figs. 38-44). The velum is sustained by irregular pegs (Fig. 44). The areolae next to the sternum have a C-shaped mor- phology (Fig. 43) due to an expansion of the vimine, also forming a central circle (Figs. 43, 44, arrow). In the foot pole there are small rounded pores arranged in radiate rows, between the last two large striae and the multiscissura (Figs. 40, 41). The rimoportula at the foot pole, located on the valve surface has a cir- cular external opening (Fig. 42) and an internal short stalked large labiate structure, transapically oriented
(Figs. 39, 40). On the head pole, the rimoportula has an outer circular aperture (Fig. 43), opening inside through a labiate sessile structure, apically oriented, and located between the valve surface and the man- tle (Fig. 38). The multiscissura has 18-20 slits (Figs.
40-42).
Ecology and distribution: Epiphytic (Al-Handal &
Wulff 2008b). The species has been recorded north of the Antarctic Peninsula: King George Island and Bransfi eld Strait (Hendey 1937, Ahn et al. 1994, Al- Handal & Wulff 2008b).
Figs 35-44. Licmophora luxuriosa. 35, 36. Valves with rimoportulae (arrows) (LM); 37-43. SEM;
37. Whole valve in internal view; 38. Head pole with sessile rimoportula in internal view; 39-41.
Internal views of foot poles with (39, 40) or without (41) rimoportula. Multiscissura and striae with small poroids are also visible; 42. Multiscissura at the end of foot pole in external view; 43.
External view of valvar surface composed of striae and large virgae; 44. TEM detailing occlusion of areolae. Rota-like structures (arrow) are present at every vimine next to the sternum. Bars: 35-37
= 10 µm; 38-42 = 5 µm; 43 = 2 µm; 44 = 30nm.
DISCUSSION
In this study, the four species of Licmophora were found in almost all sampling points, and during different years of sampling, especially the collection from Admiralty Bay. Licmophora antarctica M. Peragallo, L. belgicae, and L. gracilis were particularly frequent in that area. These results indicate the widespread distribution of Licmophora in the studied region. In other neritic areas of the Antarctic Peninsula, the genus has been frequently reported in shallow waters like in Potter Cove (Klöser 1998, Al-Handal & Wulff 2008a, 2008b), Maxwell Bay (Ahn et al. 1997), Peterson Islands and Lockroy (Peragallo 1921), Anvers Islands, Margarita Bay, and Deception Islands (Frenguelli & Orlando 1958). To date, the most abundant species in these previously investigated areas were L. antarctica M. Peragallo, L. belgicae, and L. gracilis. Furthermore, ecological studies carried out in similar regions have revealed the signifi cant contribution of Licmophora and other benthic diatoms for both the plankton and the benthic communities in shallow waters in different zones of Antarctica (Krebs 1983, Everitt & Thomas 1986, Ahn et al. 1994, Lange et al. 2007). Although no quantitative analyses have been performed in our work, Lange et al. (2007) investigated the phytoplankton ecology in Admiralty Bay during the summers of 2003 and 2004, simultaneously to our sampling stations. The authors found that the contribution of Licmophora (and other benthic
pennates) to the phytoplankton biomass was almost as large as ‘typical’ planktonic species.
Licmophora antarctica M. Peragallo is an easily recognizable species due to its elongated valve, large and rounded areolae, and coarser striation (6- 10 in 10µm) on the valve surface, also having large virgae between the striae (Peragallo 1921, Frenguelli
& Orlando 1958, Al-Handal & Wulff 2008b). The dimensions of L. antarctica M. Peragallo found in the present study overlap and even expand the data found in the original description, which reported valves 140-150 µm long and with 7 striae in 10 µm (Peragallo 1921). Al-Handal & Wulff (2008b) recorded specimens with a slightly higher number of striae (10-12 in 10µm) and a wider transapical axis (7-11 µm) (Tab. 2). Licmophora antarctica M.
Peragallo is similar to L. belgicae, though the latter is more densely striated (6-10 in 10 µm in the former, usually 10-12 in 10 µm, rarely lower; 9-10 in 10 µm in the latter) (Peragallo 1921, Frenguelli & Orlando 1958, Hustedt 1958, Simonsen 1992, Al-Handal &
Wulff 2008a). Licmophora antarctica M. Peragallo has 14-16 slits composing the multiscissura, while in L. belgicae there is a larger number (18-24).
Moreover, the valve shape is different between the two species, spathulate in L. antarctica M. Peragallo and clavate in L. belgicae.
Regarding L. belgicae, our specimens showed similar dimensions of apical and transapical axes and overall shape compared to the material investigated by previous authors (Heiden & Kolbe 1928 as Table 2.Comparative morphological data of selected species of Licmophora, and of the material investigated from the Antarctic Peninsula.
1 Honeywill (1998), 2 Wahrer et al. (1985), 3 Al-Handal et al. (2008a), 4 Al-Handal et al. (2008b), 5 Peragallo (1921), 6 Frenguelli &
Orlando (1958), 7 Heiden & Kolbe (1928) 8 Hustedt (1958). ND = no data.
L. decora, Frenguelli & Orlando 1958, Hustedt 1958, Al-Handal & Wulff 2008a as L. decora), and summarized in Tab. 2. On the other hand, the number of striae (10-12 in 10 µm, in our material) was more discrepant in relation to recorded literature elsewhere. Van Heurck (1909, as L. reichardtii var.
?) found coarser striated valves, 8.5-10 striae in 10 µm. Al-Handal & Wulff (2008a) recorded more fi nely striated specimens, ranging from 12 to 14 in 10 µm. Only Frenguelli & Orlando (1958) provide a similar range of striae - 9.5 - 10 in 10 µm - to that found in the present material.
With respect to the nomenclature of L. belgicae, Heiden & Kolbe (1928) described L. decora Heiden based on the unnamed variety Licmophora reichardtii var. ? of Van Heurck (1909, pl. 3, fi g. 1). Later, Hustedt (1958:138) considered L.
decora a synonym of L. belgicae M. Peragallo. To corroborate this nomenclatural change, we examined Heiden´s microscope slide (n. 283/43) deposited at the Friedrich Hustedt Diatom Study Centre, and the illustrations in Simonsen (1992:28, Pl. 24, Figs. 1-5).
We found valves very similar to L. belgicae, as well as identical dimensions to the description of Peragallo (1921), particularly the number of striae, 8.5 - 10.0 in 10 µm. We concluded the species is the same in both the references; therefore, L. belgicae has precedence over L. decora, as proposed by Hustedt (1958).
Licmophora luxuriosa is a large and heavily silicifi ed species with a distinctly clavate shape, besides specifi c valve features (Tab. 2). The only closely related species is L. ehrenbergii (Kützing) Grunow, though this latter has spathulate valves (Honeywill 1998). Licmophora luxuriosa has 5-7 robust striae in 10 µm, while L. ehrenbergii is more densely striated, 10-11 striae in 10µm. The fi ne morphology of the valve reveals discrete differences;
the most important is related to the velum covering of areolae. Both the species show the vimines close to the C-shaped sternum and they are modifi ed to form rota-like structures. However, in L. luxuriosa the velum is supported by irregular pegs which are also more spread out when compared to L. ehrenbergii.
The velum in this species has a higher number of pegs and arranged more regularly one to another (Honeywill 1998: 235, Fig. 3i). In both the species there is a large rimoportula possessing a short stalk at the foot pole, but sessile in the head pole. Another species bearing some resemblance with L. luxuriosa is Licmophora abbreviata Agardh, since both have the same overall shape and coarser striae than the other species (Tab. 2), except for L. ehrenbergii
(see above). However, L. abbreviata is more fi nely striated (15-17 striae in 10 µm), showing a higher number of areolae per striae (60 in 10 µm) and the multiscissura is composed of 9-13 slits (Honeywill 1998), against 18-20 slits in L. luxuriosa. Finally, the structure of areolae in L. abbreviata is characteristic, each poroid having rounded sides, and the one associated with the sternum is D-shaped, lacking the rota-like vimines as in L. ehrenbergii (Honeywill 1998) or L. luxuriosa (this paper). Our material of L. luxuriosa presented general dimensions very close to the valves reported in the original description (Heiden & Kolbe 1928, Simonsen 1992) and in the other few publications from different locations of Antarctica (Al-Handal & Wulff 2008b). Hendey (1937) reported valves as wide as 18 - 26 µm. To confi rm the measurements taken by Heiden & Kolbe (1928), the lectotype (slide 283/44) and isolectotype (slide 283/43) designated by Simonsen (1992) and deposited at the Friedrich Hustedt Diatom Study Centre were accessed. The valves examined included all the specimens photographed by Simonsen (1992, Plates 25 and 26), presenting the following dimensions: 96.7 - 121.0 µm length, 10.7 - 13.3 µm width and 6-8 striae in 10 µm. Therefore, the apical axis and the number of striae of our material fi t well in the original data of Heiden & Kolbe (1928), while the range of valve width was somewhat smaller than the range furnished in the original description (13- 21 µm). The cingulum was observed in the original material, the valvocopula being septate and fi nely striate, about 29-30 striae in 10 µm (see Plate 26, Fig. 3 in Simonsen 1992).
From the four species investigated in this work, L. gracilis is the only one that has been studied by electron microscopy previously; hence allowing a more detailed comparison of the valve morphology (Tab. 2). The number of striae of the present material showed a large range, 16 to 26 striae in 10 µm. It is important to remark that, since we found valves with such a range of striae occurring in the same sample, we did not separate the species in its varieties, namely the nominal and var. anglica. To date, the differentiation between them resides in the striae density, that is, coarse (20-23 in 10 µm) in the nominal variety and fi ner (24-26 in 10 µm) in L.
gracilis var. anglica (Peragallo 1897-1905, Hustedt 1931-1959, Witkowski et al. 2000). Our specimens also presented a complete transition of valve shape; from small spathulate valves (Figs. 21-24) to larger and clavate forms (Figs. 30-32). The fi ne morphology of L. gracilis in our material agrees with
that described in Honeywill (1998), regarding poroid structure and rimoportulae features (Tab. 2). Only the multiscissura had 7-9 elongated slits in our material, compared to the nine recorded in Honeywill (1998).
ACKNOWLEDGEMENTS
This study was part of the Brazilian Antarctic Program and the International Polar Year, funded by the Brazilian Ministry of the Environment, Ministry of Science and Technology, and National Council for Research and Development, in addition to being part of multidisciplinary projects within the International Polar Year and the Census of Antarctic Marine Life.
It is currently supported by the Instituto Nacional de Ciência e Tecnologia Antártico de Pesquisas Ambientais (CNPq proc. No. 574018/2008-5). The Center of Electron Microscope of Federal University of Paraná made the facilities available, including the electron microscopes. M.C.F. received a fellowhsip from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/REUNI). We are truly grateful to the Brazilian navy and the crew of Ary Rongel vessel for assistance with SCUBA diving. Personnel at the Friedrich Hustedt Diatom Study Centre (Germany) kindly assisted with the diatom slides examined in this study.
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